The present invention relates to an improvement of a RAM disk which performs replacement (exchange processing) upon detecting a defect in a recording block and records information by a zone CLV scheme (every time the recording track zone changes, the angular velocity changes; the angular velocity does not change in a zone).
In zone CLV (to be referred to as ZCLV hereinafter; CLV is the abbreviation of Constant Linear Velocity), the angular velocity is controlled to be constant in each zone (CAV; Constant Angular Velocity). When the recording track zone changes, the rotation speed (angular velocity) changes so that the average recording density in each zone becomes almost constant. That is, in ZCLV, CAV control is performed in each zone, and when the zone changes, the angular velocity changes accordingly.
In zone CAV (ZCAV) or modified CAV (MCAV), CAV control is performed in all zones, and when the zone changes, the read/write modulation rate changes.
For a ZCLV disk, the rotation servo of the disk need not be switched in each zone because the angular velocity does not change in each zone so that access properties similar to those of a CAV disk can be obtained in each zone. In ZCLV, when the zone changes, the angular velocity is changed (reduced in the outer zone of the disk). With this operation, a decrease in recording density on the outer side of the disk is prevented by maintaining a roughly constant average linear velocity on both inner and outer sides of the disk. Therefore, in the ZCLV disk, a memory capacity similar to that of a CLV disk and access properties similar to those of a CAV disk can be obtained.
In all writable disks of the CLV, CAV, and ZCLV schema, when a write error is generated in recording information, a dedicated replacement area is used to perform replacement (processing of writing data not in the data block where the error is generated but in a replacement area). In the CAV disk (e.g., a hard disk), the disk rotation speed is always constant. The rotation servo of the disk need not be switched in replacement (the rotation speed of a spindle motor need not be changed), and replacement is smoothly performed.
In the ZCLV disk, however, if the replacement area ranges over different rotation zones, the rotation speed of the spindle motor must be changed (because the disk is not a CAV disk). For this reason, the access speed decreases (since the rotation servo is switched every time the rotation zone changes, the time lag until the servo is seztled to a target rotation value is generated ever time the zone changes).